1. Field of the Invention
The present invention is directed to a turning device for applying a limited amount of torque to a twistable tip catheter, and more particularly to a turning device for applying torque to a torque element of a catheter with a twistable tip. The tip of the catheter can be twisted remotely by rotating with the turning device the proximal end of a torquing element internal to the catheter.
2. Description Of the Prior Art
Fiber optic catheter assemblies have increasingly been used for probing and clearing obstructions in various vessels such as arteries. The size of the vessel and the distance from the insertion point to the critical region in the vessel determine the characteristics of the catheter to be used. For example, in some situations it is desirable to insert a very thin catheter a considerable distance into a vessel. The catheter must be quite flexible so that it may be steered considerable distances through winding vessel passages.
Once the tip of the catheter reaches the critical point of the vessel passage, it is often desirable to have the tip oriented in a particular direction. It would be ideal if the tip self aligned with the obstruction, however often the tip must be remotely positioned to carry out an operation. The diameter of the optical fibers in fiber optic catheters is quite small and it is often necessary to continuously move and retarget the optical beam emanating from the optical fibers to ablate a large obstruction. Because the optical fibers are not independently directable inside the catheter, the entire end of the catheter containing the mounted optical fiber must be moved. This problem is addressed by Wells U.S. Pat. No. 4,844,062.
Commonly, the torque to rotate the tip is transmitted through the flexible outer jacket of the catheter. However, the torque applied at the proximal end of the catheter often will not be transferred to the distal end to rotate the tip. Instead the catheter will likely twist and kink under the torsional load. The friction between the catheter and its surroundings over the length of the catheter in a complex anatomy is substantial and the flexible catheter does not have enough torsional rigidity to overcome the friction and transmit torque from its proximal end to its distal end.
Flexible catheters do not have sufficient torsional stiffness to be twisted and rigid catheters do not have sufficient flexibility to be inserted into a complex passage. This problem is addressed in a continuation-in-part application disclosing a catheter with twistable tip to Hammersmark et al, filed concurrently herewith and incorporated herein by reference. The catheter contains a torque element which is attached to the distal tip of the catheter. The torque element has substantial torsional rigidity and when twisted at the proximal end imparts torque to the distal end to twist the catheter tip.
A common feature required for most twistable tip catheters is a turning means at the proximal end of the catheter. Common turning and turn limiting devices are disclosed by Frisbie et al. U.S. Pat. Nos. 4,664,113 and 4,619,263. These patents disclose screw and thread devices which impart an axial dislocation of a wire employed to steer a catheter. Another turning means is suggested by Clark et al., U.S. Pat. No. 5,114,403. The Clark torque mechanism has many parts and does not have a friction means for preventing the handle from returning to its original position when turned and then released by an operator.